my microwave is not heating up food, it is switching on but not heating?

Microwave ovens have a gizmo inside that emits energy in a similar way to a Radar transmitter. It's called a Magnetron
and you can see a picture of one here...

http://en.wikipedia.org/wiki/Magnetron

Yours may be broken or perhaps the controls are not switching it on for some reason.

Pecavi
February 2009